1. Field of the Invention
The present invention relates to an apparatus for controlling a driving signal for a motor, in particular to an improved apparatus for controlling a driving signal for a motor for converting an alternating current (AC) input signal to an instantaneous direct current (DC) signal and controlling the instantaneous DC signal, thereby driving a motor.
2. Description of the Conventional Art
FIG. 1 is a block diagram of a conventional apparatus for controlling a driving signal for a motor using a low pass filter.
As shown therein, the conventional apparatus for controlling a driving signal for a motor of a conventional converter includes a low pass filter 100 for filtering an AC input signal Xinput to a DC signal, a reference signal generator 110 for generating a reference signal Xref 110, a first subtracter 120 for subtracting a value of the reference signal Xref from a value of the DC signal, thus generating a first difference value, a first controller 130 for performing a proportional integral to the first difference value to correct the first difference value, a sine wave generator 150 for generating a sine wave to convert the corrected DC signal to the AC signal, a multiplier 140 for multiplying a value of the corrected DC signal by a value of the sine wave outputted from the sine wave generator 150, a second subtracter 160 for subtracting the AC input signal Xinput from an AC signal outputted from the multiplier 140, thus generating a second difference value, and a second controller 170 for performing the proportional integral to the second difference value to correct the second difference value.
The operation of the conventional apparatus for controlling the driving signal for the motor will be described.
First, the AC signal Xinput which is inputted to a system is filtered in the low pass filter 100, and converted to a DC signal. The first subtracter 120 generates a first difference value by subtracting a value of a reference signal Xref, outputted from the reference signal generator 110, from a value of the DC signal and outputs the first difference value to the first controller 130.
The first controller 130 performs the proportional integral to the first difference value, and thus correcting the difference value obtained the DC signal.
In order to reconvert the corrected DC signal to the AC signal, the sine wave generator 150 generates a sin wave signal, identical to a phase of the reference signal, and then the multiplier 140 multiplies the corrected DC signal by a value of the sine wave signal, thus correcting the first difference value and generating the AC signal.
The second subtracter 160 subtracts a value of the AC input signal Xinput from a value of the AC signal outputted from the multiplier 140, thus generating a second difference value which includes a phase difference between the two values.
Lastly, the second controller 170 performs the proportional integral control to the second difference signal, and thus outputs the AC signal of which size and phase are corrected to the motor.
However, the conventional low pass filter 100 only perceives a size of a signal, but not a phase thereof, thus the second subtracter 160 and the second controller 170 should be additionally provided in order to correct the phase difference, and the low pass filter 100 is not capable of corresponding a sudden change of a signal.
In addition, the second controller 170 performs controlling the signal phase in an AC condition, thus being not capable of following up a value of the reference signal which varies in accordance with a time, which is shown as a type of a phase delay, thus it is impossible to accurately control the AC input signal in accordance with the phase of the reference signal.